Mac OS X Leopard only: Today's release of Mac OS 10.5.3 added a juicy little tidbit to Address Book: the ability to automatically sync your Google contacts. After you've run Software Update and gotten 10.5.3 (and restarted your Mac), hit up Address Book's Preferences pane. At the button of the General tab, check off the "Synchronize with Google" box to get started. Be sure to back up your address book before you sync, and see the FAQ for more info. Update: Several commenters rightly point out that this capability only exists for iPhone and iPod touch owners by default, which is quite possibly a crappier move than forcing Safari onto Windows users on Apple's part. Time to switch to Linux. Update #2: Only a few hours later, a workaround surfaces. Non-iPhone/iPod touch owners, here's how to enable Google Contact sync.

Alas, I read through the comments on the hack to enable Google Contact sync without an iPhone/iTouch and it sounds problematic.